This invention relates to a method and an apparatus for detecting chemical agents, and particularly to a method and an apparatus for detecting chemical agents by a mass spectrometer and APCI (atmospheric pressure chemical ionization), best suited for detecting isopropyl methylphosphonofluoridate (hereafter referred to as sarin) and pinacolyl methylphosphonofluoridate (hereafter referred to as soman).
In recent years, there has been demand for apparatuses for detecting chemical agents to cope with chemical terrorism incidents. For detection of chemical agents, the general method is analysis of chemical agents, and the prevailing analytical method is gas chromatography/mass spectrometry (GC/MS). Normally, there have been few cases where hazardous chemical agents were detected from samples, so that the presence of toxic chemical agents is proved by detection of decomposed substances which are likely to remain as residues.
As a conventional technology with another analytical apparatus for chemical agents, liquid chromatography/mass spectrometry (LC/MS) is well known, which is used to separate and analyze volatile or nonvolatile chemical compounds.
FIG. 9 is a diagram for explaining a schematic structure of an analytical apparatus using a liquid chromatography/mass spectrometry according to prior art. The analytical apparatus according to the prior art will be described in the following. In FIG. 9, 101 denotes a liquid chromatograph (LC), 102 denotes a connection tube, 103 denotes an ion source, 104 denotes a power supply for the ion source, 105 and 109 denote signal lines, 106 denotes a mass spectrometer, 107 denotes a vacuum system, 108 denotes an ion detector, and 110 denotes a data processor.
As shown in FIG. 9, the analytical apparatus using liquid chromatography/mass spectrometry according to the prior art comprises a liquid chromatograph (LC) 101 for separating samples into separate components, an ion source 103, controlled by the power supply 104 for the ion source, for generating ions derived from sample molecules, a mass spectrometer unit 106, evacuated by a vacuum system 107, for analyzing masses of generated ions, an ion detector 108 for detecting separated ions, and a data processor 110 for processing data. The mass spectrometer includes the ion source 103, the mass spectrometer unit 106, and the ion detector 108.
In the above description, sample liquid separated into respective components by liquid chromatograph (LC) 101 is introduced through the connection tube 102 into the ion source 103 that operates under atmospheric pressure. The ion source 103, controlled by the power supply for the ion source 104 through signal lines 105, generates ions derived from sample molecules in the sample liquid. Subsequently, the generated ions are introduced into the mass spectrometer unit 106 for mass spectrometry. The mass spectrometer unit 106 is evacuated by the vacuum pumping system 107. The ions subjected to mass spectrometry are detected by the ion detector 108. Detected signals are transmitted through the signal line 109 to the data processor 110 to generate analysis data, such as mass spectra and chromatograms.
As has been described, the mass spectrometer in the analytical apparatus needs to handle ions in vacuum and therefore requires an interface means to intervene between the spectrometer and the liquid chromatograph (LC). In other words, the LC is a device which handles large amounts of water and organic solvent under atmospheric pressure, whereas the mass spectrometer (MS) is a device for handling ions under high vacuum. For this reason, it has been considered difficult to directly connect them together.
The ion mobility spectrometer (IMS) method is used chiefly in combination with ionization of a sample by a radiation source to measure the mobility of its ions in an electric field, and this is the most prevalent in-situ detection method, and there are many applied products available in Europe and the U.S. Being applicable in a smaller configuration than GC/MS or LC/MS, the IMS method has found broad usages, including those to military specifications. However, because the IMS does not identify samples in terms of m/z (mass-to-charge ratio), detectors of IMS method have a rough indication of detection results and are limited to portable use with a warning attached to the effect that soldiers must wear protective masks when an alarm sounds.
As a conventional technology related to the IMS method, one which is described in U.S. Pat. No. 6,225,6223B1 is well known.
A U.S. Patent Application titled “Substance Detection Method and Substance Detection Apparatus” was filed on May 1, 2003, under Ser. No. 10/426718, in which substances, such as explosives, are vaporized and made into negative ions which are subjected to analysis.
The above-mentioned conventional GC/MS and LC/MS methods have a problem as follows. The technology of electron ionization (EI) applies strong energy to the substance itself to be detected and therefore the substance is liable to decompose, thus producing a multitude of fragment ions, for which reason detection devices by GC/MS have difficulty in generating ions of molecular weight of the substance or of a larger molecular weight, a fact which makes it difficult to identify the sample. The GC or LC process for separation of substances to be detected prolongs a detection time.
The problem with the above-mentioned IMS method is that it has difficulty in determining the kinds of chemical agents, and that because this method permits ready response to a wide range of chemical compounds, it is difficult to decide or identify samples to be detected, resulting in a high rate of false alarms.